Certain wireless communication protocols that use Gaussian frequency-shift keying (GFSK), such as Bluetooth, Digital Enhanced Cordless Telecommunications, ZigBee, Z-Wave, etc., utilize a modulation index that controls the extent of frequency shifting or deviation which defines encoded bits; the modulation index value is nominally 0.5. Existing protocol standards, such as Bluetooth 4.2, have accuracy requirements that can be satisfied with a modulation index ranging from 0.45 to 0.55±a 10% margin of error. Error in the modulation index is mainly due to imperfections in the analog/radio frequency conversion process. Future protocol standards, such as Bluetooth 5 and higher, will require a modulation index ranging from 0.495 to 0.505±a 1% margin of error. That requirement will be difficult to achieve with current Bluetooth low energy devices, and more stringent requirements for radio frequency parts to remove variability may be cost prohibitive.
Consequently, it would be advantageous if an apparatus existed that is suitable for establishing and constraining a modulation index within a narrower range than current possible.